الفهرس 
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Abstract
LASIK has been the most popular corneal refractive surgery for myopic correction in the past decade with the emergence of the femtosecond lasers which demonstrated more predictable flap thickness and an insignificant increase in HOAs. A lot of recent techniques have developed which included WFG and WFO laser ablations. WFG ablations are based on preoperative measures of HOAs and can produce a reduction in prior existing HOAs, whereas, WFO ablations address variations in the corneal shape which decreases the induction of an oblate profile as well as other HOAs during surgery. Several studies comparing LASIK surgery outcome using different excimer laser platforms have yielded mixed results, several of which have shown no difference between them.
FOZ of the cornea was defined as the central cornea with the highest level of optical quality, contrast sensitivity and minimal aberrations. Different methods have been proposed for its measurement, such as the uniform axial power method by using the Pentacam.
In our study, we compared between WFG and WFO laser ablations by measuring the FOZ after LASIK correction for mild to moderate myopia and myopic astigmatism using the Pentacam.
Our research study was held over the period from June 2018 till December 2020. It included 100 eyes of 50 patients with myopia (± myopic astigmatism) treated with FS- Lasik surgery using two different laser platforms (WFO LASIK performed by Allegretto Wavelight EX500 and WFG LASIK performed by VISX STAR S4). Patients were divided into two groups according to the platform used, with the IOZ fixed for all patients (6mm). FOZ was measured and compared in the 2 groups three months postoperatively using the tomography based scheimpflug imaging; Pentacam HR® (Oculus, Germany).
We found no significant difference between the WFO and WFG LASIK groups as regards refractive outcomes, postoperative HOAs RMS error and SA coefficient (Z40). Whereas, a significant difference was found between the two groups as regards the mean maximal laser ablation depth and change in the corneal asphericity (ΔQ) which were significantly greater in the WFG than in WFO group.
With measurements directly obtained from the Pentacam, no significant difference was noted between the 2 LASIK groups as regards the size of FOZ 3 months following myopic LASIK, a significant negative correlation between FOZ diameter and maximal laser ablation depth and a significant positive one between FOZ diameter and postoperative corneal thickness at thinnest location were also reported.